This invention relates to a thermal cut-off fuse. More particularly, this invention relates to a self-restoring type thermal cut-off fuse which, on rise of the temperature of the ambience to a prescribed temperature, breaks the electric continuity between a pair of electric lead wires extended out of a housing in response to melting of a temperature-sensitive member contained in the housing and, on fall of the temperature of the ambience below the preset temperature, reestablishes the electric continuity between the aforementioned pair of lead wires.
Thermal cut-off fuses of the type which use the melting points of a temperature-sensitive member as their rated (prescribed) temperatures and only serve to break the electric continuity between paired lead wires at these preset temperatures are used with good results in various electric appliances susceptible to accidental overheating. A fair number of types of such thermal cut-off fuses have so far been disclosed to the art. (U.S. Pat. Nos. 4,068,204, 4,075,595, 4,075,596, 4,084,147, 4,127,839, for example.)
The thermal cut-off fuses of this class are so constructed that once the electric continuity is broken, they cannot restore the original electric continuity and have had to be discarded.
The purpose of such thermal cut-off fuses is to ensure the safe operation of electric appliances. When troubles of some form or other develop in the fused electric appliance and overheating causes the temperatures to rise beyond the prescribed temperature, the fuse melts and breaks the electric circuit. If the fuse thus broken is accidentally reset after the ambient temperature of the fuse has fallen in consequence of the cut-off of the electric appliance, then the appliance will be exposed again to the same danger (overheating) unless the causes of the trouble have been detected and eliminated. In this sense, therefore, it is only natural that such fuses are not able to restore the electric continuity once it has been broken. However, none of the thermal cut-off fuses of the conventional types can take the place of thermostats which have heretofore been used in various kinds of conventional heating devices.
A self-restoring type thermal cut-off fuse using a temperature-sensitive member capable of taking the place of the conventional thermostat would prove highly useful.
In the first place, the thermal cut-off fuse of this type generally permits a substantial reduction in size, improves the space factor of the portion thereof enclosing the heat-sensitive circuit and, moreover, dispenses with the otherwise inevitable use of a massive, expensive metal part such as a bimetal strip and, therefore, proves to be economical. Above all, the fact that the temperature-sensitive member excels in temperature properties contributes immensely to the reliability of the circuit.
One object of this invention is to provide a self-restoring type thermal cut-off fuse which breaks the electric continuity of lead wires on rise of the temperature of the ambience thereof to the prescribed temperature and, after the aforementioned temperature has fallen below the preset temperature, reestablishes the electric continuity.